The Hubble's Empty Patch of Sky

In 1995, astronomer Robert Williams made a request that his colleagues thought was wasteful. He asked to point the Hubble Space Telescope at a tiny, seemingly empty patch of sky near the Big Dipper — a dark sliver no bigger than a grain of sand held at arm's length. For ten consecutive days, Hubble gathered light from that one unremarkable spot where no one expected to find anything at all.…